the eye unaided by any optical instrument that alters the power of vision or alters the apparent size or distance of objects; "it is not safe to look directly at the sun with the naked eye"
increased pressure in the eyeball due to obstruction of the outflow of aqueous humor; damages the optic disc and impairs vision (sometimes progressing to blindness)
capable of being reached only with great difficulty or not at all
not capable of being obtained; "a rare work, today almost inaccessible"; "timber is virtually unobtainable in the islands"; "untouchable resources buried deep within the earth"